Blink and You’ll Miss It (But This Sensor Won’t)

Unlike the traditional sensors found in wearable devices that need to be directly attached to the skin, noncontact sensors can measure various physiological parameters from a distance. These sensors use technologies such as infrared, ultrasound, and optical systems to gather data without the need for direct skin contact. By using methods such as these, it is possible to significantly enhance user comfort, as there is no need for adhesives, straps, or tight fittings that can cause discomfort or irritation, especially during prolonged use. Furthermore, noncontact sensors experience less wear and tear which may increase their useful lifespan.

Electrostatic sensors have captured a great deal of interest for their ability to detect nearby objects and small motions in a contact-free manner. When an object, such as a part of the human body, comes near the sensor, it alters the local electric field, which the sensor can detect and measure. These properties are ideal for a number of applications in wearables, however existing electrostatic sensors suffer from some problems. In particular, they are finicky about the types of objects that they can detect, have a limited window of operation before needing to be charged, and they can be very challenging to fabricate.

A novel electrostatic sensor recently described by researchers at the East China University of Science and Technology has a unique design that allows it to overcome the issues experienced with present technologies. And since the new sensor is transparent, it proved to be perfect for use as an eyelash proximity detector in a pair of blink-tracking glasses created by the team.

Fabrication of the device is very simple and only requires three components — thin sheets of fluorinated ethylene propylene (FEP), an electrically conductive film, and a plastic substrate. The FEP layer is used for sensing, while the conductive film transmits signals from the sensor to external devices. The plastic substrate serves only to give the sensor mechanical strength.

Once the FEP material is charged, it produces an external electrostatic field. As objects come into close proximity to this sensing layer, it causes electrical current to flow through the conductive film, indicating the presence of those objects. It proved to be quite an accurate sensor, and was demonstrated to be capable of detecting objects at ranges of 2 to 20 millimeters.

It was also shown that the sensors can hold their charge for long periods of time. Even after 90 hours had passed, the FEP layer maintained 98% of the initial electrical charge it was given. Moreover, after 3,000 sensing cycles, the device was still operational.

The researchers were able to solve all of the problems that they set out to address, so they incorporated one of their sensors into the lens of a pair of eyeglasses. By monitoring the distance of the eyelashes from the sensor, it was demonstrated that blinks could be detected. In an experiment, it was shown that Morse code could be decoded using the glasses. This method could similarly be used to help those with certain disabilities to communicate, or to detect drowsiness while driving.